Your spit can pinpoint your age to within five years, making it by far the most accurate age test yet found. This discovery could help identify how old crime scene suspects are, as well as reveal people's true biological ages.

This remarkable finding was made by researchers at UCLA. They found that the DNA contained in a person's saliva undergoes changes as a person gets older. One of the building blocks of DNA experiences a process known as methylation, which alters its appearance over time and can be used to estimate precisely how old a person is.

Head researcher Dr. Eric Vilain explains:

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"Our approach supplies one answer to the enduring quest for reliable markers of aging. With just a saliva sample, we can accurately predict a person's age without knowing anything else about them. While genes partly shape how our body ages, environmental influences also can change our DNA as we age. Methylation patterns shift as we grow older and contribute to aging-related disease.

The researchers tried out their age test on saliva from 34 sets of identical twins between the ages of 21 and 55, then again on 31 men and 29 women whose ages ranged from 18 to 70. They focused on two of the three genes that are most heavily affected by the methylation process. Using just those two genes out of the three billion or so that make up the complete human genome, they were able to provide a generally accurate five-year estimate for each person's age.

There are two big possibilities for this breakthrough. In terms of practical applications, it would be hugely useful to know the rough age of a criminal suspect, and saliva can often be found at a crime scene. That said, there is a slight drawback - not everyone's age actually lines up with their amount of methylation. As such, a criminal suspect with an unusual methylation rate could leave behind misleading spit, which could make for some truly bizarre court cases.

However, while it might be a headache for law enforcement, it's still useful to know methylation rates even when it doesn't correlate with a person's age. That's because methylation does line up with a person's biological age, and that can be more important than a person's chronological age. Knowing a person's methylation rate could help predict the onset of age-related diseases, and it could help explain why some people with a young chronological age - but presumably a relatively old biological age - occasionally succumb to diseases generally associated with older patients.